Zirconia zircon silicon refractory



Patented Nov. 14, 1939 I ZIRCONIA ZIRCON SILICON REFRACTORY John D.Morgan, South Orange, N. J., assignor to Power Patents Company,Hillside, N. J., a corporation of Maine No Drawing. Application March17, 1937, Serial No. 131,456

3 Claims. (01. 106-9) The present invention relates to hightemperaefiicient of heat conductivity of ths calories ture resistantbondedrefractories, and more parper centimeter per second per degree C.The ticularly to an improved zirconia-silicon refracconductivity of highgrade ferro-silicon is only tory and process of making the same.slightly less than that of pure silicon. Metallic Refractories made ofzirconia and zircon silicon and high grade ferro-silicon, however, 8bonded together with phosphoric acid are disare subject to chemicalattack at high temperaclosed in my United States Patent No. 1,809,249.tures, and are not therefore adapted for use as Refractories made ofzircon and silicon bonded such in high temperature furnace construction.together with phosphoric acid are disclosed in Another disadvantage ofmetallic silicon and 10 the United States patent of John D. Morgan,ferro-silicon is that both of these materials swell 10 W. G. Bjordstedtand R. E. Lowe, No. 1,811,242. when subjected to continuous heating athigh The herein described invention is an improvetemperatures. Themineral zircon is a very efiiment on such refractories. cient heatinsulator, and possesses a low co-effi- The primary object of thepresent invention cient of expansion per degree of change in temis toprovide a high temperature resistant reperature. While the highshrinkage character- 15 fractory which is chemically basic and whichistics of zirconia can be balanced to some extent possesses highelectrical resistance, high therby mixing therewith silicon "or ferrosilicon, mal-conductivity, and a small co-efficient of v which expandwith heat, it has been found that thermal expansion or contraction inuse. a strong bond between these materials can not With the above andother objects and features be obtained simply by bonding agents such as20 in view, the invention is hereinafter described phosphoric acidalone. The refractory of the and particularly defined by theaccompanying present invention is based in part on the disclaims. coverythat a suitable bond between zirconia A composition of the aggregatewhich is emand silicon or ferro-silicon is only obtainable ployed informing the refractory of the present by employing a refractory, asdistinguished from 25 invention is substantially as follows: a metallic,bonding medium, thepreferred bond- 16-66 parts of zirconia, crushed topass through ing agent being zircon phosphate produced by a 200 meshscreen; 2-8 parts of zircon, crushed reaction between about equalproportions of minto pass through a 200 mesh screen; 76-20 parts eralzircon and phosphoric acid.

of 75% ferro-silicon, about 70% of which is An example of the preferredmethod of mak- 3O crushed to pass through a 10 mesh and remain ing therefractory which forms the substance of on a 20 mesh screen, while 15%is crushed to the present invention will now be described: pass througha 20 mesh screen and remain on Zirconia is crushed and finely ground sothat a 40 mesh screen, and 15% is crushed to pass the material will passthrough a 200 mesh screen.

through a mesh screen and remain on a 60 Native zircon (zirconiumsilicate) is also milled to 35 mesh screen. As a bonding agent, about3-9 pass through a 200 mesh screen. Ferro-silicon parts (average 6parts) by weight of 85% ortho- (preferably 75 %-85% silicon.) iscoarsely ground phosphoric acid is employed. so that about 70% will passthrough a 10 mesh Accord n t he pr ferred method of screen and beretained on a 20 mesh screen, and

40 ing the Y, there is Obtained a thoroughly so that about 15% will passthrough a 20 mesh 40 bonded and de s high te p resistant screen and beretained on a 40 mesh screen, while re ac y v g a h g electricalresistance, about 15% will 'pass through a 40 mesh screen a hi melting pa high t al du and be retained on a 60 mesh screen. About 40 tivity, asmall co-efilcient of thermal expansion to 42 parts by weight of thefinely divided zir- 45 or contraction at high temperatures, and whichconia is admixed with about 6 parts by weight of 45 is suflicientlybasic to resist chemical attack when the milled grain zircon, and themixture is wetted p y in Contact w basic slaes or in basic with water toacreamy consistency, after which atmospheres. 6 parts by weight of 85%orthophosphate acid zirconia is known for its highly refractory is addedto the wetted mixture. This mixture is properties, but its use islimited by reason of digested for a period of several hours at a tem- 50its high shrinkage when used under furnace perature in the neighborhoodof 200 F., the temconditions. This shrinkage characteristic ofzirperature during the latter part of the digestion conia at hightemperature is apparent even when period being raised to about 350 F.until the conthe zirconia has been electrically fused and resistency ofthe mixture has increased to that of ground. Pure metallic siliconpossesses a coa thick paste. The digested zirconia-zircon- 55 phosphoricacid paste is then well stirred while undergoing dilution with water toincrease its fluidity to a milky consistency. About 48 to 50 parts ofthe coarsely ground ferro-silicon are now added to the milky partiallydigested zir-coniazircon-phosphoric acid mixture. The resulting mixtureis thoroughly agitated and stirred for a brief period, and is thenallowed to digest for several hours at an elevated temperature until theconsistency has thickened to a degree suitable for casting. In somecases, the period of digestion is continued until the digested mix turehas assumed a solid state. In either case, during the latter part of thed sting period, the mixture is subjected for a short pe iod to a strongvacuum (20 inches or more) and thoroughly evacuated until all signs ofgas cbul on from the mixture have ceased. In cases where the mixture isdigested to dryness, the solid product of this operation is reground andmilled. to a suitable size (so that about 26% will through an 80 meshscreen) fter which the ground product is wetted with water andrehydrated to a molding consistency, 3. e., a consistency that willretain its shape when hand molded.

Refractories as prepared above may be cast or molded into various shapesand furnaces, hearths and the like, for embed resistance wire to form arefractory electric heating element. The shapes into whic refractory iscast or molded are preferably and fired at temperatures approximatingthose at which the refractory is to be finally used.

The invention having been thus described what I claim as new is:

1. A method of making a bonded refractory which comprises mixing about16-66 parts by weight of finely crushed zirconia (through 200 mesh) with2-8 parts by weight of milled grain zircon, wetting the mixture withwater and about 6 parts by weight of phosphoric acid to a creamyconsistency, reducing the mixture to the consistency of a thick paste bydigestion for several hours at a temperature ranging from about 200 350ER, adding water to increase the fluidity of the mixture and thoroughlyadmixing therewith about 76-20 parts by weight of coarsely groundferrosilicon (l0-60 mesh), digesting the mixture while agitating it andwhile heat drying the mixture to a suitable consistency for casting andshaping, drying and heat hardening the product.

2. The method of claim 1 in which the heating operation which followsthe addition of ferrosilicon to the mixture is continued until theproduct is dry, after which the product is pulverized and thereafterrehydrated to a suitable consistency for molding.

3. The method of making a high temperature resistant refractory whichcompri about 40 parts by weight of finely o 1e, zirconia with about 6parts by weight 0; milled. grain Zircon, wetting the m xture with waterand about 6 parts by weight of phosphoric acid and digesting the mixturefor several hours at 200-350 F., while increasing its consistency tothat of a thick paste, again wetting the mixture with water and addingthereto about 45-50 parts by weight of coarsely ground ferro-silicon,thoroughly agitating the mixture and shaping, drying and heat hardeningthe product.

JOHN D. MORGAN.

mixing

